Variable width slit operating mechanism



Lb U 311mm mm July so, 1968 G. M. STIFF 3,394,977

VARIABLE WIDTH SLIT OPERATING MECHANISM Filed Feb. 17, 1964 2 Sheets-Sheet 1 July 30, 1968 5. M. STIFF 3,394,977

VARIABLE WIDTH SLIT OPERATING MECHANISM Filed Feb. 17, 1964 2 Sheets-Sheet 2 17V VENTOQ Geofirey Malcolm Scifl.

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United States Patent 3,394,977 VARIABLE WIDTH SLIT OPERATING MECHANISM Geoffrey Malcolm Stiff, Monbulk, Victoria, Australia, assignor to Commonwealth Scientific and Industrial Research Organization, East Melbourne, Victoria, Australia, a body corporate Filed Feb. 17, 1964, Ser. No. 345,523 Claims priority, application Australia, Feb. 18, 1963, 27,496/63 6 Claims. (Cl. 350-271) ABSTRACT OF THE DISCLOSURE A mechanism for controllably varying the width of a slit in instruments for the determination of spectral data. A movable slit defining member is supported by flexure strips parallel to and in the same plane as a fixed slit defining member. The movable slit defining member is controlled by an operating arm and caused to move in a direction parallel to the longitudinal dimension of the slit, which in turn flexes the strips causing changes in their effective length such that the movable slit defining member has a component of motion transverse to the longitudinal direction of the slit.

This invention relates to variable width slit operating mechanisms, and especially to such mechanisms which are normally associated with slits for optical instruments and instruments employed for the determination and measurement of absorption and emission spectra, mass spectra and the like.

Slits of the type referred to above are usually bounded by adjustable slit defining members, which normally take the form of two accurately parallel, opposed knife edges, one or both of which can be moved relatively to the other so as to vary the separation distance between them. In conventional variable slit operating mechanisms the movable slit defining member is usually mounted on guide rails and is actuated by a micrometer screw. Roller mounted slit defining members and pivoted linkages are also sometimes employed. Such mechanisms generally suffer from the phenomena of lost movement, backlash and the so-called stick-slip motion, which are usually associated with screw-threaded mechanisms.

It is an object of this invention to provide an improved mechanism for controllably varying the adjustment of the width of slits of the type referred to above? A further object of the invention is to provide a mechanism to controllably vary the widths of two slits in uriison.

According to the invention there is provided a mechanism for controllably varying the width of a slit comprising a base frame, a fixed slit defining member secured on the base frame, a movable slit defining member supported from the base frame and in the same plane as the fixed slit defining member by means of two parallel, resiliently flexible arms, and operating means arranged to displace the movable slit defining member in the plane of the said slit defining members in a direction substantially parallel to the longitudinal dimension of the slit, characterised in that said displacement causes both supporting arms to be flexed, whereby the changes in the effective lengths of the arms so produced cause the movable slit defining member to be subjected to a motion in the same plane having a component in a direction transverse to the longitudinal dimension of the slit.

In a preferred embodiment of the invention, there are two pairs of slit defining members and a common operating means which is adapted to vary the widths of both slits.

Preferably the supporting arms of the two movable slit defining members are equal in length, whereby the widths of the two slits are varied equally on flexure of said arms.

In order that the invention may be more fully and completely understood, a presently preferred practical embodiment will now be described by way of example with reference to a mechanism or instrument for simultaneously and equally varying the widths of two slits, which is often required in instruments such as spectrophotometers. This instrument is described with reference to the accompanying drawings, in which:

FIGURE 1 is a schematic diagram of the optical system of a monochromator, showing a typical use of a double slit;

FIGURE 2 is a perspective view from the front of the double slit mechanism when fully assembled (i.e. wholly enclosed within its casing);

FIGURE 3 is a plan view of the double slit mechanism with the front cover removed, shown in the position where both slits are closed;

FIGURE 4 is a view similar to that of FIGURE 3, but shown in the position where both slits are open;

FIGURE 5 is a cross-section along line 5-5 in FIG- URE 3;

FIGURE 6 is a cross-section along line 66 in FIG- URE 3;

FIGURE 7 is a cross-section along line 7-7 in FIG- URE 4;

FIGURE 8 is a cross-section along line 8-8 in FIG- URE 4;

FIGURE 9 is a perspective view of the two movable slit defining members and their associated support arms and operating or flexure strip, which form a unitary structure; and

FIGURE 10 is an enlarged detail showing the portion of the actuating sleeve carrying the roller which brings about the flexure of the supporting arms.

Referring now to the drawings, it is seen that the double slit operating mechanism is mounted on a circular baseplate 11, which has a raised flange 12 around its perimeter. The flange 12 is provided with two diametrically opposed shoulders 13, 14, to each of which a slit defining knife blade 15, 16 is secured by means of screws which pass through elongated slots in the knife blade, thus permitting a limited degree of adjustment thereof relative to their supports 13, 14. These knife blades 15, 16 constitute the fixed slit defining members of each slit.

The movable slit defining members are also constituted by knife blades 17, 18 which are attached to a rectangular auxiliary frame (shown in FIGURE 9), which is itself mounted on the base plate 11 within the confines of the peripheral flange 12. The auxiliary frame is made up of two rigid metal support bars 19, 20, the ends of which are connected together by means of two relatively thin, flat spring members 21, 22 of a resilient metal, suchas Phosphor bronze. The spring members 21, 22 are rigidly attached to the bars 19, 20, being housed or set in suitable slots at the places indicated by reference 25 and secured in position there by soldering. The bars 19, 20 and spring members 21, 22 together form a substantially rectangular, open, box-like frame. Each spring member is rigidly clamped at its mid-portion 26 to the vertical face of one of a pair of diametrically opposed pillars 27, 28 which are integral with the peripheral flange 12, whereby the auxiliary frame is suspended so that the upper faces of the bars 19, 20, are coplanar with the. face of the peripheral flange 12, and the lower faces of the bars 19, 20 are a small distance above the surface of the base plate 11. The knife blades 17, 18 which form the movable slit defining members are attached to the support bars 19, 20 in such a way that, when the auxiliary frame Patented July 30, 1968 is in its nOrmaL'undistorted, rectangular state, each movable slit defining member abuts against its corresponding fixed slit defining member 15, 16, whereby the two slits of the instrument are closed. This is the position shown in FIGURE 3 of the drawings.

A third spring member 29 joins the mid-points of the two support bars 19, 20, and is again rigidly attached to each bar in the same manner as that described above. An operating arm 30 is pivotally mounted at one of its ends on a vertical axis 31 which is located near the perimeter of the base plate 11. The arm 30 extends through a slot 32 in the support bar 20 into the region 33 bounded by the support bars 19, 20 and the spring members 22, 29. The portion of the arm 30 lying in the region 33 adjacent the spring member 22 has an arcuate outline 34 which is convex towards the spring member 22. The arm 30 is connected to the spring member 29 by means of a straight, rigid link 35. Both ends of the link 35 are provided with needle points, which are adapted to engage a mating socket 36 in the operating arm 30 and a locating aperture 37 in the spring member 29.

In order to minimize the effect of small discrepancies between the lengths of the spring members 21, 22 and 29, and in other components, which may occur during manufacture, it is desirable that the auxiliary frame is not perfectly rectangular, when the mechanism is in the unoperated condition, i.e. when the slits are closed. It is therefore preferable that the length of link 35 is increased so that, when the slits are closed, the ends of the spring members 21 and 22 are displaced a small distance (of the order of from the perfectly rectangular position.

An actuating ring or sleeve 38 surrounds the flange 12 of the base-plate 11, and is freely rotatable relatively thereto. The ring 38 is provided with an inwardly projecting arm 39, which is substantially parallel to the base plate and carries at its end, on a vertically disposed shaft 40, a small roller 41, which runs on ball bearings and is adapted to engage the outer arcuate or cammed edge 34 of the operating arm 30. The cammed outline 34 of the operating arm 30 and the disposition of the roller 41 are so chosen that, as the actuating ring 38 is rotated relatively to the base plate 11, the roller 41 displaces the operating arm 30 in such a way that the link 35 is moved by the arm substantially in a straight line which is the longitudinal axis of the link. This displacement of the link 35 causes flexure of the spring member 29, and is transmitted therefrom to the support bars 19, 20, which in turn cause flexurc of the spring members 21, 22 which join the ends of the two support bars. Thus, while the link 35, through which movement is transmitted from the ring 38 to the auxiliary frame, is displaced in a direction substantially parallel to the two slits defined, respectively, by the knife edges 16 and 18, and and 17, this cauech a relatively small lateral movement of the support bars 19, due to the effective shortening of the spring members 21, 22 and 29, whereby the slits are opened by moving their knife edges further apart.

The actuating ring 38 is provided with a peg or abutment 42 to limit the extent of the rotation of the ring. A calibrated scale 43 is marked on the outer surface of the ring 38 and the flanged base plate 11, to indicate the size of the slit openings for any particular angular position of the ring, and it will be readily seen that the shape of the operating arm and its disposition relative to the roller 41 can be modified to provide a large number of different relationships between the angle of rotation of the ring and the size of the slit openings. A front cover plate 44 is provided for the instrument, which ensures that dust and other impurities do not get into the mechanism. The cover has two apertures 45, 46 corresponding to the location of the slits, and is attachable to the base plate 11 by means of screws 47 which engage locating bosses 48, the cover being spaced from the bosses 48 by spacers 49.

It will be apparent that, provided the frame 11 is symmetrical and the link is disposed at all times along the center line of the frame which bisects all the spring members (and is thus parallel to both support bars), both slits will open and close in complete synchronism. Moreover, the amount of movement of each slit will be equal to that of the other, provided the spring members 21 and 22 flex equally, i.e., are of the same material and of equal dimensions.

Slit opening mechanisms according to the present invention have a number of important advantages over presently known and used apparatus of this type. Thus, in the case of the instrument described above, it is possible to vary the widths of two slits equalZ-y and in perfect synchronism, which is often very important, as, for example, in spectrophotometry. Secondly, the movable slit defining members move for a considerable distance in a direction generally parallel to the longitudinal dimension of the slit, for a quite small transverse movement, i.e. transverse to the longitudinal dimension of the slit (in the case of the instrument described above, the ratio between these two movements is approximately 8:1). This enables very accurate adjustment of the slit widths to be obtained. Also, the motion of the movable slit defining members, being determined by the column flexure of the spring members of the auxiliary frame, does not suffer from the effects of stick-slip motion and backlash which are always a source of worry with mechanisms involving screwthreaded movements, pivoted linkages or roller mounted slit defining members. The spring members are flexed well within the elastic deformation range and, although the relationship between the lateral and longitudinal motion of the movable slit defining members is not linear, this relationship can be easily calibrated and is accurately reproduced whenever the spring members are flexed (at least until metal fatigue sets in).

It is to be understood that the practical embodiment of the invention described above is not to be construed as limiting the scope of the invention in any way. Clearly, other operating means can be provided for flexing the frame which controls the movement of the movable slitdefining members, the same operating principle based on column flexure may be used in a mechanism for varying the width of only one slit, etc. These and other modifications and variations are accordingly to be considered as being within the spirit and scope of this invention as disclosed and claimed herein.

I claim:

1. A mechanism for controllably varying the width of a slit, said mechanism comprising a base frame, a fixed slit defining member integral with the base frame, a movable slit defining member parallel to said fixed slit defining member supported from the base frame and in the same plane as the fixed slit defining member by means of two parallel, resiliently flexible arms, and operating means adapted to displace the movable slit defining member in the plane of the said slit defining members and in a direction substantially parallel to the longitudinal dimension of the slit such that said displacement causes both supporting arms to be flexed, whereby the changes in the effective lengths of the arms so produced cause the movable slit defining member to be subjected to a motion in the said plane having a component in a direction transverse to the longitudinal dimension of the slit.

2. A mechanism for controllabl-y varying the widths of two slits in unison, said mechanism comprising a base frame, two fixed slit defining members integral with the base frame, two movable slit defining members each parallel to the respective fixed slit defining members each supported from the base frame in the same plane as the respective fixed slit defining members by means of two parallel, resiliently flexible arms, and located adjacent to the corresponding fixed slit defining members, and operating means adapted to displace each of the movable slit defining members in the plane of the said slit defining members and-in a direction substantially parallel to the longitudinal dimension of each slit such that said displacement causes both supported arms associated with each movable slit defining member to be flexed, whereby the changes in the effective lengths of the arms so produced cause each movable slit defining member to be subjected to a motion in the said plane having a component in a direction transverse to the longitudinal dimension of the respective slit.

3. A mechanism for controllably varying the widths of two slits in unison and by equal amounts, said mechanism comprising a base frame, two fixed slit defining members integral with the base frame, two movable slit defining members each parallel to the respective fixed slit defining members each supported from the base frame and in the same plane as the respective fixed slit defining members by means of two parallel, resiliently flexible arms and located adjacent to the corresponding fixed slit defining members, said supporting arms being equal in length and of the same modulus of elasticity, and operating means adapted to displace each of the movable slit defining members in the plane of the said slit defining members and in a direction substantially parallel to the longitudinal dimension of each slit such that said displacement causes both supporting arms associated with each movable slit defining member to be flexed, whereby the changes in the effective lengths of the arms so produced cause each movable slit defining member to be subjected to a motion in the said plane having an equal component in a direction transverse to the longitudinal dimension of the respective slit.

4. A mechanism for controllably varying the widths of two slits in unison and by equal amounts, said mechanism comprising a base frame, two fixed slit defining members integral with the base frame, two movable slit defining members each parallel to the respective fixed slit defining members each supported from the base frame and in the same plane as the respective fixed slit defining members by means of two parallel, resiliently flexible arms and located adjacent to the corresponding fixed slit defining members, said supporting arms being equal in length and of the same ;modulus of elasticity, and operating means including a lever pivoted on the base frame and being adapted, on being turned about its pivot axis, to transmit a deflecting force to the supporting arms, said lever having a cammed edge which is engaged by a manually actuable cam follower, the position of which relative to said lever can be varied, whereby the angular disposition of said lever causes a deflecting force to be exerted by it on said supporting members, thereby to displace each of the mov. able slit defining members in the plane of the said slit defining members and in a direction substantially parallel to the longitudinal dimension of each slit such that said displacement causes both supported arms associated with each movable slit defining member to be flexed, whereby the changes in the effective lengths of the arms so produced cause each movable slit defining member to be subjected to a motion in the said plane having an equal cornponent in a direction transverse to the longitudinal dimension of the respective slit.

5. A mechanism as claimed in claim 4, wherein the base frame is circular in plan and the cam follower is carried by a ring which surrounds the base frame and is rotatable thereon, said ring and said base frame being provided with a calibrated scale indicative of the changes in slit opening resulting from the rotation of the ring relative to the base frame.

6. A mechanism as claimed in claim "5, wherein each of the movable slit defining members is mounted on a rigid bar which is secured to the ends of the respective supporting arms, the midpoints of the two bars beingconnected by a flexible metal strip which is engaged at its midpoint by one end of a perpendicularly disposed rigid link, the other end of which is acted on by said pivoted lever, whereby rotation of said lever about its pivot point causes a deflecting force to be transmitted to the flexible strip, causing in turn flexure of the supporting arms.

References Cited UNITED STATES PATENTS 3,098,408 7/1963 Cary 350-271 3,242,796 3/1966 Strickler 350-271 JEWELL H. PEDERSEN, Primary Examiner. RONALD L. WIBERT, Assistant Examiner. 

